Semiconductor memory devices are a major component of modern electronic devices. They can be found, for instance, in computers, portable communication devices, and embedded systems, to name but a few.
Semiconductor memory devices can be categorized as volatile or nonvolatile based on whether they retain stored data when disconnected from power. Volatile semiconductor memory devices do not retain stored data when disconnected from power, while nonvolatile semiconductor memory devices do retain stored data when disconnected from power. Examples of volatile semiconductor memory devices include static random access memory (SRAM), dynamic random access memory (DRAM), and synchronous DRAM (SDRAM). Examples of Nonvolatile semiconductor memory devices include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable and programmable ROM (EEPROM), flash memory, phase change RAM (PRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), and ferroelectric RAM (FRAM).
Flash memory has gained popularity in recent years due at least to the proliferation of portable electronic devices requiring nonvolatile data storage or kinetic shock resistance. There are two major categories of flash memory with varied configurations and operating principles, known as NAND flash memory and NOR flash memory. NAND flash memories tend to have greater integration density and faster erase and write times compared with NOR flash memories, while NOR flash memories tend to have faster read times.
Because of their different performance characteristics NAND and NOR flash memories may be used for different purposes. For instance, NOR flash memory is commonly used to store information requiring fast access, such as program code due to its fast read time, while NAND is commonly used to provide mass data storage due to its high integration density.